The Environment Protection Agency (EPA) requires that specialty gas producers selling standards labeled as an EPA Protocol Gas to follow the latest requirements.
Specialty gas producers cannot sell EPA Protocol Gases if they are not assayed with NIST-traceable analytical reference standards. Currently, in order to assay nitrogen dioxide (NO2) gas mixtures as EPA Protocol Gases, the use of PRMs from VSL is required. NIST has indicated they are in the process of developing an NO2 SRM, but there is no timeline in place for when this development will be completed.
In addition, the EPA requests your opinion and any information you may have on (1) the long-term stability of the NO2 gas mixtures in the Luxfer cylinders and in standard passivated aluminum cylinders and (2) what concentration may be the most stable, so that this information may be communicated to our monitoring agencies.
Stability of NO2 gas mixtures
It has also come to the EPA’s attention that in standard passivated aluminum cylinders, the NO2 gas concentration can be unstable and degrade over a relatively short period of time. In light of this knowledge, VSL uses SGSTM (superior gas stability) aluminum cylinders from Luxfer for PRM concentrations less than 250 ppm to maintain gas concentration stability. These cylinders have a proprietary interior surface that helps to prevent reactions and concentration degradation.
The EPA would like to work with the specialty gas producers to determine the long-term stability of NO2 gas mixtures in these cylinders and at what concentration ranges they may be the most stable.
In the future, NO2 EPA protocol gases will be assayed as part of the Ambient Air PGVP. These assays will help to determine the long-term stability of the certified concentrations of these gas mixtures.